Combinatorial gene regulation by Bmp and Wnt in zebrafish posterior mesoderm formation

Combinatorial signaling is an important mechanism that allows the embryo to utilize overlapping signaling pathways to specify different territories. In zebrafish, the Wnt and Bmp pathways interact to regulate the formation of the posterior body. In order to understand how this works mechanistically, we have identified tbx6 as a posterior mesodermal gene activated by both of these signaling pathways. We isolated a genomic fragment from the tbx6 gene that recapitulates the endogenous tbx6 expression, and used this to ask how the Bmp and Wnt signaling pathways combine to regulate gene expression. We find that the tbx6 promoter utilizes distinct domains to integrate the signaling inputs from each pathway, including multiple Tcf/LEF sites and a novel Bmp-response element. Surprisingly, we found that overexpression of either signaling pathway can activate the tbx6 promoter and the endogenous gene, whereas inputs from both pathways are required for the normal pattern of expression. These results demonstrate that both Bmp and Wnt are present at submaximal levels, which allows the pathways to function combinatorially. We present a model in which overlapping Wnt and Bmp signals in the ventrolateral region activate the expression of tbx6 and other posterior mesodermal genes, leading to the formation of posterior structures.     

Characterization of Promoter Activities of Four Different Japanese Flounder Promoters in Transgenic Zebrafish

An important consideration in transgenic research is the choice of promoter for regulating the expression of a foreign gene. In this study several tissue-specific and inducible promoters derived from Japanese flounder Paralichthys olivaceus were identified, and their promoter activity was examined in transgenic zebrafish. The 5′ flanking regions of the Japanese flounder complement component C3, gelatinase B, keratin, and tumor necrosis factor (TNF) genes were linked to green fluorescence protein (GFP) as a reporter gene. The promoter regulatory constructs were introduced into fertilized zebrafish eggs. As a result we obtained several stable transgenic zebrafish that displayed green fluorescence in different tissues. Complement component C3 promoter regulated GFP expression in liver, and gelatinase B promoter regulated it in the pectoral fin and gills. Keratin promoter regulated GFP expression in skin and liver. TNF gene promoter regulated GFP expression in the pharynx and heart. TNF promoter had lipoplysaccharide-inducible activity, such that when transgenic embryos were immersed lipopolysaccharide, GFP expression increased in the epithelial tissues. These 4 promoters regulated the expression of GFP in different patterns in transgenic zebrafish.     

Too much interference: injection of double-stranded RNA has nonspecific effects in the zebrafish embryo

We have investigated the ability of double-stranded RNA (dsRNA) to inhibit gene expression in a vertebrate, the zebrafish, Danio rerio. Injection of dsRNA corresponding to the T-box gene tbx16/spadetail (spt) into early wild-type embryos caused a rapid and dramatic loss of tbx16/spt mRNA in the blastula. mRNAs from the papc, tbx6, and gata1 genes, which depend on tbx16/spt function for their expression, were reduced, apparently mimicking the spt mutant phenotype. However, mRNAs from a number of genes that are unaffected by the spt mutation, such as beta catenin, stat3, and no tail, were also lost, indicating that the "interference" effect of tbx16/spt dsRNA was not restricted to the endogenous tbx16/spt mRNA. We compared the effects of injecting dsRNA from the zebrafish tbx16/spadetail, nieuwkoid/bozozok, and Brachyury/no tail genes with dsRNA from the bacterial lacZ gene. In each case the embryos displayed a variable syndrome of abnormalities at 12 and 24 h postfertilization. In blind studies, we could not distinguish between the effects of the various dsRNAs. Consistent with a common effect of dsRNA, regardless of sequence, injection of dsRNA from the lacZ gene was likewise effective in strongly reducing tbx16/spt and beta catenin mRNA in the blastula. These findings indicate that, despite published reports, the current methodology of double-stranded RNA interference is not a practical technique for investigating zygotic gene function during early zebrafish development.     

Gene silencing in Xenopus laevis by DNA vector-based RNA interference and transgenesis

A vector-based RNAi expression system was developed using the Xenopus tropicalis U6 promoter, which transcribes small RNA genes by RNA polymerase Ⅲ. The system was first validated in a Xenopus laevis cell line, designing a short hairpin DNA specific for the GFP gene. Co-transfection of the vector-based RNAi and the GFP gene into Xenopus XR1 cells significantly decreased the number of GFP-expressing cells and overall GFP fluorescence. Vector-based RNAi was subsequently validated in GFP transgenic Xenopus embryos. Sperm nuclei from GFP transgenic males and RNAi construct-incubated-sperm nuclei were used for fertilization, respectively. GFP mRNA and protein were reduced by -60% by RNAi in these transgenic embryos compared with the control. This transgene-driven RNAi is specific and stable in inhibiting GFP expression in the Xenopus laevis transgenic line. Gene silencing by vector-based RNAi and Xenopus transgenesis may provide an alternative for ＇repression of gene function＇ studies in vertebrate model systems.     

An Apo-14 promoter-driven transgenic zebrafish that marks liver organogenesis

Several transgenic zebrafish lines for liver development studies had been obtained in the first decade of this century, but not any transgenic GFP zebrafish lines that mark the through liver development and organogenesis were reported. In this study, we analyzed expression pattern of endogenous Apo-14 in zebrafish embryogenesis by whole-mount in situ hybridization, and revealed its expression in liver primordium and in the following liver development. Subsequently, we isolated zebrafish Apo-14 promoter of 1763 bp 5'-flanking sequence, and developed an Apo-14 promoter-driven transgenic zebrafish Tg(Apo14: GFP). And, maternal expression and post-fertilization translocation of Apo-14 promoter-driven GFP were observed in the transgenic zebrafish line. Moreover, we traced onset expression of Apo-14 promoter-driven GFP and developmental behavior of the expressed cells in early heterozygous embryos by out-crossing the Tg(Apo14: GFP) male to the wild type female. Significantly, the Apo-14 promoter-driven GFP is initially expressed around YSL beneath the embryo body at 10 hpf when the embryos develop to tail bud prominence. In about 14-somite embryos at 16-17 hpf, a typical "salt-and-pepper" expression pattern is clearly observed in YSL around the yolk sac. Then, a green fluorescence dot begins to appear between the notochord and the yolk sac adjacent to otic vesicle at about 20 hpf, which is later demonstrated to be liver primordium that gives rise to liver. Furthermore, we investigated dynamic progression of liver organogenesis in the Tg(Apo14: GFP) zebrafish, because the Apo-14 promoter-driven GFP is sustainably expressed from hepatoblasts and liver progenitor cells in liver primordium to hepatocytes in the larval and adult liver. Additionally, we observed similar morphology between the liver progenitor cells and the GFP-positive nuclei on the YSL, suggesting that they might originate from the same progenitor cells in early embryos. Overall, the current study provides a transgenic zebrafish line that marks the through liver organogenesis.     

Endosperm-specific expression of green fluorescent protein driven by the hordein promoter is stably inherited in transgenic barley (Hordeum vulgare) plants

The expression of green fluorescent protein (GFP) and its inheritance were studied in transgenic barley (Hordeum vulgare L.) plants transformed with a synthetic green fluorescent protein gene [sgfp(S65T)] driven by either a rice actin promoter or a barley endosperm-specific d-hordein promoter. The gene encoding phosphinothricin acetyltransferase (bar), driven by the maize ubiquitin promoter and intron, was used as a selectable marker to identify transgenic tissues. Strong GFP expression driven by the rice actin promoter was observed in callus cells and in a variety of tissues of T0 plants transformed with the sgfp(S65T)-containing construct. GFP expression, driven by the rice actin promoter, was observed in 14 out of 17 independent regenerable transgenic callus lines; however, expression was gradually lost in T0 and later generation progeny of diploid lines. Stable GFP expression was observed in T2 progeny from only 6 out of the 14 (43%) independent GFP-expressing callus lines. Four of the 8 lines not expressing GFP in T2 progeny, lost GFP expression during T0 plant regeneration from calli; one lost GFP expression in the transition from the T0 to T1 generations and three lines were sterile. Similarly, expression of bar driven by the maize ubiquitin promoter was lost in T1 progeny; only 21 out of 26 (81%) independent lines were Basta-resistant. In contrast to actin-driven expression, GFP expression driven by the d-hordein promoter exhibited endosperm-specificity. All seven lines transformed with d-hordein-driven GFP (100%) expressed GFP in the T1 and T2 generations, regardless of ploidy levels, and expression segregated in a Mendelian fashion. We conclude that the sgfp(S65T) gene was successfully transformed into barley and that GFP expression driven by the d-hordein promoter was more stable in its inheritance pattern in T1 and T2 progeny than that driven by the rice actin promoter or the bar gene driven by the maize ubiquitin promoter.     

A cyp19a1b‐gfp (aromatase B) transgenic zebrafish line that expresses GFP in radial glial cells

Aromatase is an enzyme that catalyzes the synthesis of estrogen in gonads and brain. Teleost fish express aromatase (AroB) strongly in the brain facilitating its detailed examination. To understand the function of AroB in the brain, we generated transgenic zebrafish that expresses green fluorescent protein (GFP) driven by the brain aromatase cyp19a1b promoter. GFP was found in the radial glial cells of transgenic larvae and adult fish that overlap with AroB immunoreactivity in the correct temporal and spatial pattern. GFP was also coexpressed with radial cell marker BLBP, but was not in neurons. In addition, GFP expression in the radial glial cells was stimulated by estrogen, same as endogenous AroB expression. Thus, this transgenic line faithfully mimics the regulation of AroB expression in radial glial cells. It provides a powerful tool to further characterize progenitor radial cells in adult and developing fish and to evaluate estrogenic activities of xenoestrogens and phytoestrogens. genesis 47:67–73, 2009. © 2008 Wiley‐Liss, Inc.     

B-lymphocyte targeting of gene expression in transgenic mice with the immunoglobulin heavy-chain enhancer.

A hybrid gene containing rabbit beta-globin structural sequences (-9 to +1650), and a chicken conalbumin gene promoter (+62 to -102) in the place of the beta-globin promoter (upstream from -9), was inactive in 5 different transgenic mouse line. Adding the mouse immunoglobulin heavy-chain (IgH) enhancer to this construction specifically stimulated expression in B-cells. These results show that IgH enhancer is specifically active in B-cells. Expression of the hybrid gene was low compared to the endogenous immunoglobulin heavy and light-chain genes. Substituting the mouse immunoglobulin kappa light-chain gene (Ig kappa) promoter (+4 to -800) for the heterologous conalbumin promoter was not sufficient to restore gene expression to level of the endogenous genes. In addition to the reproducible B cell expression, we also found inheritable unexpected expression in certain tissues, which varied from line to line.     

Zebrafish enhancer trap line recapitulates embryonic aquaporin 1a expression pattern in vascular endothelial cells

Aquaporin 1 (Aqp1) is a water channel protein, expressed widely in microvascular endothelial cells and implicated in mammalian tumor angiogenesis. However, its developmental expression has not yet been characterized in great detail. An enhancer trap screen was performed using a Tol2-derived GFP reporter in zebrafish embryos. An insertional Et(GBT-B1)tpl1 line was identified that has reporter insertion in the vicinity of the aqp1a gene. We further characterized the embryonic expression pattern of this GFP reporter line, as well as that of endogenous aqp1a. Both endogenous aqp1a and reporter GFP expression were restricted to the vascular endothelial cells within the dorsal aorta, cranial, intersegmental and other secondary vessels, but were absent in the axial venous vasculature. In addition, endogenous aqp1a expression was observed in both primitive and definitive hematopoietic erythroid progenitors, as well as in the otic vesicle, swim bladder, pneumatic duct, intestine and a subset of neurons within the retina and the midbrain-hindbrain region. We further show that gata1 and etsrp/etv2 function is required for hematopoietic and endothelial aqp1a expression, respectively. Aqp1a expression is restricted to endothelial and erythroid cells during early embryogenesis. The transgenic Et(GBT-B1)tpl1 line recapitulates endogenous endothelial aqp1a expression. Because currently very few reporter lines can differentiate between arterial and venous endothelial cells, the Et(GBT-B1)tpl1 transgenic line and characterization of the aqp1a expression pattern will be useful for future studies of endothelial and arterial-venous differentiation.     

Generation and characterization of a GFP transgenic rat line for embryological research

Model organisms expressing fluorescent proteins are important tools for research. The present study was performed to generate and characterize a new line of green fluorescent protein (GFP) transgenic rats for use as a model in experimental embryological research. We injected a GFP expression vector into 135 zygotes of the Sprague-Dawley (SD) rat strain. Embryo transfer of 103 surviving embryos resulted in the production of 35 offspring (33.9%) and two of them were transgenic (5.7%). Two transgenic rat lines that ubiquitously express GFP under the control of the cytomegalovirus-enhancer/beta-actin (CAGGS) promoter were generated by breeding. We studied the main embryological parameters of one these GFP transgenic lines. Homozygous GFP-transgenic females have the same ovulation and superovulation rates as wild type (WT) females. Transgenic embryos reached blastocyst stage in vitro and developed in vivo after embryo transfer without decrease in their developmental ability compared to the control group. The genotype of the parents determined the onset of GFP expression in preimplantation embryos. When the GFP gene is derived from the transgenic female parent, fluorescence was detected in oocytes and in embryos of all further stages of development. When the GFP gene is inherited by the transgenic male parent, GFP was only expressed from the blastocyst stage on. GFP-transgenic rats represent a valuable tool to mark embryos for many embryological studies such as transgenesis, gene expression patterns during early development, embryo aggregation for analysis of the distribution of cells in chimeric embryos and nuclear transfer to confirm the origin of the cloned offspring.     

Topo II alpha reporter mice reveal proliferative regions in the epidermis and small intestine

We investigated topoisomerase II alpha promoter activity in epithelia. In confluent human keratinocytes the promoter (-557 to+90 bp) was upregulated by oncogenic Ras. In transgenic mice expressing GFP via the promoter, GFP expression in undamaged epidermis was confined to growing hair follicles. GFP was also expressed in intestinal crypts. GFP expression was upregulated in epidermis following wounding or phorbol ester treatment. In each situation GFP expression correlated with high endogenous topoisomerase II alpha expression and high proliferation. The mice therefore provide a useful model for non-invasive imaging of regions of high proliferation in normal or damaged epidermis.     

Development of a heat shock inducible gfp transgenic zebrafish line by using the zebrafish hsp27 promoter

In the present study, a zebrafish hsp27 promoter was isolated and used to develop heat shock inducible gfp transgenic zebrafish. The endogenous hsp27 mRNAs were constitutively expressed from 4 hpf and increased in several regions of brain, heart and somites in early embryogenesis until 24 hpf. Subsequently, the expression was reduced significantly but maintained in the heart and ears. Heat shock induced hsp27 mRNAs in the blastoderm from 6 hpf and later in somites, branchial arches and several regions of brain. Similarly in hsp27-gfp transgenic zebrafish, constitutive GFP expression was observed from 11 hpf. GFP expression was mainly in the skin cells and increased to the peak level at 7 dpf, followed by a reduction. The constitutive GFP expression in the heart was initiated from 50 hpf and maintained even in the adult fish. After heat shock, GFP expression was mainly induced in the muscle in addition to a mild increase in the skin and heart. The early stages of the embryos were more sensitive than late stages as the time required for induced GFP expression in the muscle is shorter. Thus, the hsp27-gfp transgenic line generally recapitulates the expression pattern and heat shock inducibility of endogenous hsp27 RNAs. We also tested the potential of using the hsp27-gfp transgenic zebrafish embryos for heavy metal induction and demonstrated the inducibility of GFP expression by arsenic; this pattern of induction was also supported by examination of endogenous hsp27 mRNA.     

Transgenic labeling of the zebrafish pronephric duct and tubules using a promoter from the enpep gene

In recent years the zebrafish has become a popular model system to study organ development and disease. To facilitate these studies, genetic tools are required which allow to modify and manipulate gene expression in organs of interest. Here we describe a zebrafish 2kb glutamyl aminopeptidase (enpep) promoter fragment, and show that it can drive gene expression specifically in the kidney during early and late development. We established a stable transgenic line using this promoter fragment that has specific GFP expression in pronephric ducts and tubules starting at 20h post-fertilization.